FIG. 1 is a cross-sectional view showing a prior art electromagnetic valve device 1. FIG. 2 is a cross-sectional view showing a guide body 5 with which the electromagnetic valve device 1 is equipped. The electromagnetic valve device 1 is an electromagnetic open/close valve that opens and closes a valve passage 3 formed in a housing 2 by a valve body 4. The guide body 5 is provided to the housing 2, and the valve body 4 fits in one axial direction end portion 12 of the guide body 5. A stationary magnetic pole body 6 made of a magnetic material is fixed to the other axial direction end portion of the guide body 5. A plunger 7 made of a magnetic material fits in the guide body 5 so that it is provided between the valve body 4 and the stationary magnetic pole body 6.
A coil 8 is provided so that it surrounds a portion of the guide body 5 on the side of the other axial direction end portion. A yoke 9 is provided so as to cover the coil 8 from radially outside and from the both sides in the axial direction. When an electric current is not supplied in the coil 8, the plunger 7 is pressed by a spring member 10 that is provided between the stationary magnetic pole body 6 and the plunger 7, thereby closing the valve body 4 and closing the valve passage 3. When an electric current is supplied in the coil 8, a magnetic circuit that passes through the stationary magnetic pole body 6, the plunger 7, and the yoke 9 is formed, and, then, the plunger 7 is magnetically fixed to the stationary magnetic pole body 6, thereby opening the valve body 4 and opening the valve passage 3.
In this electromagnetic valve device 1, when an electric current is supplied in the coil 8, since the plunger 7 is magnetically fixed to the stationary magnetic pole body 6, a magnetic circuit that passes through the guide body 5 in a portion at which the stationary magnetic pole body 6 and the plunger 7 oppose each other is undesirable and should not be formed. Therefore, a portion 11 of the guide body 5 that covers the portion at which the stationary magnetic pole body 6 and the plunger 7 oppose each other must be made of at least a nonmagnetic material. For this reason, the guide body 5 typically is entirely made of a nonmagnetic material.
FIG. 3 is a sectional view showing another prior art guide body 5A. The guide body 5A of FIG. 3 is similar to the guide body 5 of FIGS. 1 and 2. Therefore, similar reference numerals are assigned to corresponding portions to only explain different portions. Since the guide body 5 of FIGS. 1 and 2 is entirely a nonmagnetic material as mentioned above, there is a portion 15 of the guide body 5 that is made of a nonmagnetic material and that is positioned in the magnetic circuit which passes through the stationary magnetic pole body 6, the plunger 7, and the yoke 9. Therefore, the portion 15 adds resistance to the magnetic circuit, and a fixing force from the coil 8 that magnetically fixes the plunger 7 to the stationary magnetic pole body 6 becomes less. In order to resolve this inconvenience, in place of the guide body 5 shown in FIGS. 1 and 2, the guide body 5A shown in FIG. 3 must be used.
A portion 16 of this guide body 5A on the side of the one axial direction end portion is made of a magnetic material, and a portion 17 on the side of the other axial direction end portion is made of a nonmagnetic material. Therefore, the portion 11 that covers the portion at which the stationary magnetic pole body 6 and a plunger 7 oppose each other is made of a nonmagnetic material, and the portion 15 that is positioned in the magnetic circuit which passes through the plunger 7 and the yoke 9 is made of a magnetic material. Accordingly, the above-mentioned inconvenience can be resolved. Such a guide body 5A using the portion 16 made of a magnetic material, and the portion 17 made of a nonmagnetic material is shown, for example, in Japanese Laid-Open Patent Application No. 2002-231546.
In the guide body 5A shown in FIG. 3, the pulling force between the stationary magnetic pole body 6 and the plunger 7 can be increased as mentioned above. However, since the axial direction end portion 12, which serves as a portion for guiding the valve body 4, is also made of a magnetic material, metal powders that have entered into the valve body during operation of the electromagnetic valve body may be pulled to the axial direction end portion 12. In such a case, the metal powders may cause adverse effects, and there is a possibility of causing degradation of the seating characteristic over the seat of the valve body 4.